1. Field of the Invention
The present invention relates to a non-volatile semiconductor device, in which a memory block of deficient erasure can be automatically replaced with a redundant memory block.
2. Description of the Related Art
Since a flash memory, which is one type of non-volatile semiconductor device, is featured by repeatedly rewriting data and holding storage data even after a power source is turned off, it is frequently used as an external storage device. However, data cannot be overwritten in the flash memory. Therefore, in order to write new data in the flash memory, the storage data is erased, and then, the new data is written in the flash memory.
In the case where data cannot be erased in a certain memory block when data stored in a memory cell is erased in accordance with an erasure command, a deficient erasure status representing deficient erasure is merely output from the memory block. Therefore, a next erasure command is transmitted to the deficient memory block also at the time of next data erasure, thereby outputting a deficient erasure status.
Thus, in the case where a part of a storage region is broken in the above-described flash memory, the contents in a decoder are rewritten in order to prevent any decoding in the region, thereby enhancing the reliability (see, for example, claim 1 and FIG. 1 in Japanese Patent Application Laid-open No. 188712/2001 entitled “Storage Device Control Method”).
However, since the reliability is enhanced by the entire system for controlling a writing operation or the like in a memory chip in the flash memory disclosed in Japanese Patent Application Laid-open No. 188712/2001, it is necessary to markedly change the design of the entire storage device, and further, to change the design of each of the flash memories.